The cost of high grade bookbinding has become so expensive that it puts books beyond the reach of many readers, and forces people to wait until the book is put out into a "paperback" edition.
This invention is directed to methods for making books with plastic covers and in ways that lend themselves to automation and with reduced binding costs so that the books with covers that extend beyond the edges of the pages, and that are stiff enough to support the book without folding under the pages and breaking, can be made at reasonable cost.
The cover is made of plastic and preferably from a plastic that can be heated by an electric field in a period of very short duration and to a temperature at which the plastic is soft enough to flow so that the rules of a die can be brought down to displace the plastic around the entire outline of the cover except for a very thin tear section which holds the cover in place but which permits the cover to be torn from the web quickly and easily. The plastic has sufficient resilience so that the edge along the tear springs back to leave a smooth even edge around the full perimeter of the cover. The die can be, and preferably is, made with curved rules at the corners of the cover so that the corners of the book are rounded in the finished book.
The invention has its greatest utility in making high grade books where the cover extends beyond the edges of the pages and this requires that the plastic used be stiff enough so that when the book is finished the edges of the cover that extend below the bottom edges of the pages of the filler are sufficiently stiff to support the weight of the filler without folding under and breaking as occurs when books are made with paper covers extending beyond the edges of paper.
In the preferred method, the leaves constituting the filler for the book are assembled and then stabilized; that is, held in assembled relation by connecting them together along the spine portion of the filler so that the filler can be handled in subsequent operations without resorting to the use of clamps to hold the pages in the desired assembled relation.
With the method of this invention, the material used for the cover is often plasticized. By compounding the plastic with plasticizers, greater control over the stiffness and other physical properties of the plastic can be obtained. Where a problem of plasticizer migration is presented, a barrier coat or other means are used to prevent the plasticizer in the cover from migrating into the adhesive used on the pages of the filler. This migration is usually a gradual process but over a long period can greatly weaken the adhesive so that the book no longer has the necessary strength to hold the filler securely in the cover.
Another feature which lends itself to automation is the use of "electromagnetic adhesive". This term is used to cover constructions of the adhesive which permits adhesive to be activated by subjecting it to an alternating electromagnetic field. Adhesive can be made "electromagnetic" by including in the adhesive metal powder, especially ferrous metal powder, which is strongly heated by an alternating magnetic field. Electromagnetic adhesive can also be provided by coating both sides of a thin metal foil or strip with adhesive coating both sides of a thin metal foil or strip with adhesive which is softened by heat generated within the metal by a magnetic field adjacent to the metal. Such a foil or strip with adhesive on both sides has the advantage that the adhesive on the side which faces the book cover can be one which is particularly effective with the particular plastic used for the cover, and the adhesive on the other side can be adhesive which is particularly effective with paper but not so effective with plastic. It is, of course, necessary that both adhesives bond securely to the metal and they should also bond to each other if the construction is one where the metal is perforated to permit interlocking of the adhesives through the perforations of the metal.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.